Recently, mobile traffic has been rapidly increased in accordance with the spread of smart phones and tablet PCs and activation of high capacity multimedia communication. It is expected that mobile traffic will be increased twice every year. Since most of the mobile traffic is transmitted through a base station, communication service providers are faced with the problem of serious network load. In this respect, the communication service providers have increased network facilities to process traffics which are increased, and have quickly commercialized the next generation mobile communication standard that can efficiently process high capacity traffic such as mobile WiMAX and long term evolution (LTE). However, another solution will be required to handle the amount of traffics which will be more increased in the future.
Device to device (D2D) communication refers to the distributed communication technology that directly transfers traffic between adjacent nodes without using infrastructure such as a base station. In a D2D communication environment, each node such as a portable terminal discovers another user equipment physically adjacent thereto and transmits traffic after setting communication session. In this way, since D2D communication may solve traffic overload by distributing traffic concentrated into the base station, the D2D communication may have received attention as the element technology of the next generation mobile communication technology after 4G. For this reason, the standard institute such as 3GPP or IEEE has proceeded to establish the D2D communication standard on the basis of LTE-A or Wi-Fi, and Qualcomm has developed their own D2D communication technology.
It is expected that the D2D communication contributes to increase throughput of a mobile communication system and create new communication services. Also, the D2D communication may support proximity based social network services or network game services. The problem of link of a user equipment located at a shade zone may be solved by using a D2D link as a relay. In this way, it is expected that the D2D technology will provide new services in various fields.
The D2D communication technologies such as infrared communication, ZigBee, radio frequency identification (RFID) and near field communications (NFC) based on the RFID have been already used. However, since these technologies support communication only of a specific object within a limited distance (about 1 m), it is difficult for the technologies to be regarded as the D2D communication technologies strictly.
Although the D2D communication has been described as above, details of a method for transmitting data from a plurality of D2D user equipments with the same resource have not been suggested.